Control system



June w, 1958 H. A. BREEDING ETAL 2,838,717

' CONTROL SYSTEM Filed Dec. 30, 1955 g 3 1 l A; o l J Inven'ior-s:

Harold A. Breeding Ermzs+ C. MQLr'H' by, Thrzir Afior-nay United StatesPatent CONTROL SYSTEM Harold A. Breeding, Hendersonville, N. C., andErnest C. Marti, Chagrin Falls, Ohio, assignors to General ElectricCompany, a corporation of New York Application December 30, 1955, SerialNo. 556,729

13 Claims. (Cl. 317--22) ()ur invention relates to control systems forseries lighting circuits.

In series lighting circuits, a number of lamps are connected in serieswith one another and supplied with a substantially constant current froma substantially constant potential source through the agency of atranslating device which converts a constant voltage supply into aconstant current supply. The most commonly employed translating devicefor accomplishing this result is a floating coil variable impedancetransformer although various networks such as the monocyclic square maybe used. Such a device, in its attempt to maintain constant currentoutput, will generate extremely high output voltages when the continuityof the series lighting circuit supplied thereby is interrupted. Suchhigh voltages may damage the circuit components of the system and are adefinite shock hazard to anyone coming in contact with the circuit.

In order to avoid these high open circuit voltages, it has heretoforebeen proposed to de-energize the series lighting circuit in response toopen circuits caused by apparatus failures other than lamp failures.Lamp failures have been provided for by connecting across each lamp acutout which, upon a lamp failure, completes a circuit about thedefective lamp. If an open circuit is caused by a lamp failure, it isdesirable to maintain energization of the series lighting circuit untilthe cutout connected across the defective lamp can function to shortcircuit the lamp and re-establish the series circuit. For open circuits,due to causes such as the breaking of an overhead wire forming part ofthe series circuit, it is desirable to de-energize the circuit quickly,and if possible,-before the wire falls to the ground. Usually, a delayperiod of from one to one and one half seconds between the occurrence ofan open circuit and the operation of a circuit breaker for de-energizingthe lighting circuit is sutficient to give the protection desired andsufficient time within which the lamp cutouts may function to shortcircuit defective lamps. Such a protective systcm is shown and describedin United States Letters Patent 2,324,875, Justin Peterson and FrederickA. Weigel,

granted July 20, 1943.

Open air arcs, incandenscent lamps, and various forms of vapor lamps maybe used in such lighting circuits. The employment of straight seriesconnected vapor lamps may result in the failure of cutouts associatedwith operative lamps or, if a cutout fails to operate, in an indicationof an open circuit when in fact current has ceased to flow in the serieslighting circuit because one or more arcs have become extinguished dueto a voltage dip in the source of supply and cannot be re-struck at theusual ignition voltages because of the heated condition of the lamps.This situation will be appreciated from a consideration of the operationof a mercury vapor lamp having a gas filling such as argon in order tofacilitate are striking and the subsequent vaporization of the mercuryfilling of such a lamp. Such a mercury vapor lamp may becomeextinguished if a 25% subnormal operating voltage exists for a period oftime as short as four cycles of the source of supply. Once heated such amercury vapor lamp requires a much higher starting voltage than issuitable for starting it in its cold condition. Such a mercury arc lampmay require from 200 to 300 volts for are striking when cold whereaswhen heated due to a prior operation thereof it may require severalthousand volts for are striking. Due to the ionizable gas filling inthese lamps and its low pressure when the lamp is cold, the 200 to 300volts required for are striking may drop to as low as 20 volts uponignition of the arc and thereafter increase after about five minutes toan operating value of about volts when the pressure in the lamp hasincreased to about one atmosphere due to the vaporization of the mercurytherein. Ordinarily, about 25 such lamps are connected in a serieslighting circuit and supplied with about 3.2 ampercs by a constantcurrent transformer having an open circuit voltage of about 6300 volts.Each lamp in such circuit may be provided with a short circuiting cutoutwhich is intended to breakdown at a lamp voltage of from 450 to 600volts. Consequently, if a series lighting circuit includes straightseries connected mercury lamps of the type above described and theselamps have been brought to their operating temperature before theybecome extinguished due to a dip in line voltage, any attempt tore-ignite them may result in premature cutout failures indicative oflamp failures whereas in fact the difficulty is due to the high strikingvoltage required to rc-ignite them in their heated condition resultingfrom previous operation.

it is an object of our invention to prevent a protective de-energizationof a series lighting circuit immediately following an interruption inthe current flow therein and to provide for such protectivede-energization if energization of the circuit produces no current flowtherein.

It is another object of our invention to provide for the re-energizationof a series lighting system a predetermined time interval after theinterruption of current flow therein has caused its de-energization sothat previously ignited lamps may cool sufficiently to facilitate arestriking at lower applied voltages.

It is also an object of our invention to provide a series are lightingsystem which is de-energized both after a short interval following itsenergization without current flow and immediately upon the interruptionof a current flow once established and which is re-energized after atime interval sulficient for the arc lamps therein to cool to normalstarting conditions once current has flowed in the circuit and given anindication that the open circuit condition may be due to arcextinguishment and not due to some mechanical failure requiringattention and repair.

It is a further object of our invention to provide a control system fora series lighting circuit in which protection is provided againstovervoltage occurring due to mechanical failures in the system and inwhich a delay period is imposed for re-energizing the system after eachde-energization thereof in response to interruption of current flowtherein to prevent premature cutout failures occurring across lampshaving a high starting voltage when heated due to their previousoperation.

For a better understanding of our invention, together with other andfurther objects thereof, reference should be had to the followingdescription taken in connection With the accompanying drawing, and itsscope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a diagrammatic illustration ofthe circuit elements and their interconnection in an electrically resetsystem embodying our invention; and Fig. 2 is a diagrammaticrepresentation of a like system embodying a mechanically resetcomponent.

type which converts a substantially constant voltage supply into asubstantially constant current supply for the vapor lamps 9 which areconnected in direct series circuit with one another in the lightingcircuit 1. These lamps may be of the mercury type above described andhave like operating characteristics. They have been indicated by Xs andonly four have been shown although it is to be understood that thecircuit may include any reasonable number of these lamps and theextension of the circuit for this purpose has been indicated by thedotted lines which complete the lighting circuit as illustrated in thedrawing. Each lamp is provided with a cutout which may form part of thelamp structure or be associated with the socket for the lamp. In thedrawing, one of these cutouts has been illustrated at it) connected inshunt to one of the lamps 9 and it will be understood that each of thelamps will normally be provided with such a cutout. One suitable type ofcutout comprises a dielectric film or barrier which breaks down when thevoltage applied thereto by electrodes in engagement with the filmexceeds a predetermined value. Upon breakdown of the dielectric film ofthe cutout, a circuit is completed in shunt to a defective lamp so thatthe continuity of the series circuit and the ignition of the remaininglamps in this circuit is not interrupted.

The energization of operating winding 8 of contactor 7 is controlled bytwo timing means which are selectively energized by a series relay 11having an operating winding 12, normally open contacts 13 and normallyclosed contacts 14. V The operating winding 12 of this series relay isconnected to be responsive to current flow in the lighting circuit. Inthe arrangement illustrated, this has been accomplished by energizing itthrough a series insulating transformer 15 having its primary winding 16connected in the series lighting circuit and its secondary winding 17connected to its operating winding 12. In view of the fact that thevapor lamps have at times a tendency to generate a direct currentcomponent of current flow in the lighting circuit, a condenser 18 hasbeen connected in series with the lamps to prevent the flow of thiscurrent. In order to increase the sensitivity of series relay 11, acondenser 19 has been connected in series circuit with its winding 12.It will be understood that the arrangement is such that upon currentflow in the lighting circuit, series relay 11 will be energized to closeits normally open contacts 13 and open its normally closed contacts 14and that upon no current how in the lighting circuit or upon aninterruption of the current flow therein, this relay will assume theposition illustrated in the drawing opening its normally open contacts13 and closing its normally closed contacts 14.

One of the above-noted timing means, which acts as a protective device,is controlled through the normally closed contacts 14 of series relay11. This timing means comprises a thermal switch 20 and a lock-in relay21. The other above-noted timing means, which constitutes a recyclingdevice, is controlled through the normally open contacts 13 of seriesrelay 11 and comprises a time delay reclosing relay 22 and a holdingrelay 23 associated therewith. The first timing means operates todisconnect the constant current transformer from its supply conductorsin response to an interruption in the lighting circuit due to someapparatus failure other than a lamp failure, and the second timing meansoperates to disconnect the primary of the constant current transformerfrom its supply conductors when current flow in the lighting circuit isinterrupted after having once been established therein. Under thecontrol of this second timing means, the primary of the constant currenttransformer will again be connected to the source of supply apredetermined time after the interruption of current how in the lightingcircuit so that the lamps therein may be re-ignited after a suitablecool period following their extinguishment and the opening of thelighting circuit which may have resulted from a dip in line voltage orother circuit disturbance. If, however, the opening of the lightingcircuit has been the result of some circuit failure, such as a brokenconductor, the arrangement is such that after the second timing meanshas recycled in order to re-energize the circuit, the absence of currentflow therein will then operate the first timing means to disconnect theprimary of the constant current transformer from its source of supply ina manner requiring a resetting operation thereof before the lightingcircuit can again be energized by connecting the primary of the constantcurrent transformer to its source of supply.

Thermal switch 20 has normally closed contacts 24 and normally opencontacts 25 which are controlled by a thermal element 26 which acts on abimetal switch member 27 which constitutes a common contact for bothcontacts 24 and 25. This thermal switch is so constructed as to operatewithin a second or a second and a half after its thermal element hasbeen energized so that within this period of time its contacts 24 areopened and its contacts 25 are closed. In order to limit arcing at itscontacts, bimetal switch member 27 may have a snap action in itsmovement from one position to the other to control the making andbreaking of circuits through its contacts 24 and 25.

Lock-in relay 21 has an operating winding 28, normally closed controlcontacts 29, normallyclosed reset contacts 3t! and normally open lock-incontacts 31.

Time delay reclosing relay 22 has an operating winding 32 normallyclosed contacts 33 and an adjustable delay mechanism 34 which permitsits contacts 33 to be opened immediately on the energization of itswinding 32 but which delays the closing of these contacts by a timeperiod having a duration of the order of 7 to 10 minutes although longerdelay times maybe used. In the an rangement illustrated, the delaymechanism 34 has been indicated as of the dash pot type althoughobviously other mechanisms may be employed for imposing a time delay inthe closing of contacts 33 of this relay.

The holding relay 23 associated with the time delay reclosing relay 22has an operating winding 35, normally open contacts 36 and normally opencontacts 37.

Control power for operating the components of the control circuit issupplied through a switch 38 which connects the control circuit withenergizing conductors 39. These energizing conductors are connected tothe secondary 46 of a control transformer 41 having its primary windingconnected across supply conductors 5. These supply conductors may beenergized at 2400 volts from a 60 cycle source of supply and the controltransformer may be constructed to provide a control voltage of the orderof 200 to 220 volts. The control switch 38 has been illustrated as ahand operated switch although it is to be understood that in manyinstances it will be the switching means of a time switch or of aphotoelectric relay which may be employed for turning the serieslighting circuit on or off in accordance with a desired program.

The interconnection of the above-described components into the system ofFig. 1 will now be described in connection with the operation of thesystem.

The lighting circuit 1 may be energized by closing control switch 38.Closure of this switch connects the operating winding 8 of contactor 7across energizing conductors 39 through the normally closed contacts 33of time delay reclosing relay 22 and normally closed control contacts 29of lock-in relay 21. Contactor 7 consequently closes its contacts 6 andconnects primary winding 4 of constant current transformer 3 to supplyconductors 5 for energization from the source of supply. Constantcurrent transformer 3 is thus energized and through its secondarywinding 2 and the load conductors connected thereto suppliesenergization to lighting circuit 1. If, due to a line fault or circuitfault other than a defective lamp, no current flows in the lightingcircuit, series relay 11 will not be energized and will remain in theposition illustrated in the drawing with its normally closed contacts 14closed and its normally open contacts 13 open. Consequently, thermalswitch will be energized from conductors 39 through the normally closedcontacts 14 of series relay 11 through a circuit including the normallyclosed contacts 33 of time delay reclosing relay 22, the normally closedcontacts 24 of thermal switch 20, its thermal element 26, resistor 43,normally closed contacts 14 of series relay 11 and normally closedresetting contacts of lock-in relay 2.1. After a time delay period ofone to one and one half seconds, thermal switch 20 will close itscontacts 25 energizing winding 28 of lock-in relay 21 from conductors 39through a circuit including the normally closed contacts 33 of timedelay reclosing relay 22. When relay 21 picks up, it completes its ownholding circuit across conductors 39 through its normally open contacts31. it also opens its normally closed control circuit contacts 29 andtie-energizes winding 8 of contactor 7 which thereupon opens itscontacts 6 to deenergize the lighting circuit 1. It also opens its resetcontacts 39 to tie-energize thermal switch 20 which thereupon opens itscontacts 25 and closes its contacts 24 for a SIlbSQUIllZ operation Sincelock-in relay 21 remains energized, through its contacts 31, theoperating winding 8 of contactor 7 cannot again be connected forenergization until operating winding 28 of lock-in relay 21 isde-energized by opening control switch 38. Upon de-energization, lock-inrelay 21 returns to the position illustrated in the drawing and thisrelay under the control of thermal switch 20 is again conditioned foranother protective operation such as has been described.

If as a result of the energization of lighting circuit 1 by closingcontrol switch 38, current flows in the lighting circuit, series relay11 will be energized and close its normally open contacts 13 and openits normally closed contacts 14. The opening of normally closed contacts14 ale-energizes the protective timer 2021 which cannot consequentlyoperate as above described. Closing of normally open contacts 13 ofseries relay 11 will cause holding relay 23 to close its contacts 36 and37 by connecting its operating winding across conductors 39 throughnormally closed control contacts 29 of lock-in relay 21 and normallyclosedcontacts 33 of time delay reclosing relay 22. Closure of contacts36 of holding relay 23 will connect the operating Winding 32 of timedelay reclosing relay 22 across conductors 39 through the normally opencontacts 13 of series relay 11, which are now closed, normally closedcontacts 29 of lock-in relay 21 and the now closed normally opencontacts 37 of holding relay 23. Thereafter, if for some reason currentceases to flow in lighting circuit 1, series relay ill will becomedeenergized closing its normally closed contacts 14 and opening itsnormally open contacts 13. The opening of contacts 13 of series relay 11de-energizes windings 32 and 35 of time delay reclosing relay 22 andholding relay 23. Relay 23 immediately opens its contacts 36 and 37 butcontacts 33 of relay 22 will not close until timing mechanism 34 permitsthem to close from 7 to 10 minutes after the deenergization of relay 22.This results in the de-energization of operating winding 8, of relay 7and the consequent removal of power from the lighting circuit by theopening of contacts 6. During this timing period of relay 22, the timingof thermal switch 20 is prevented by the opening of its operatingcircuit at contacts 33 of relay 22 and at contacts 37 of relay 23.After'the time interval imposed by relay 22, contacts 33 thereof willclose to energize operating winding 8 of contactor 7 by connecting itacross conductors 39 through switch 38, contacts 33 of relay 22 andcontacts 29 of relay 21. Contactor 7 will thus close its contacts 6 andsecure another energization of the lighting circuit 1 through constantcurrent transformer 3. The time period imposed by relay 22 before thelighting circuit 1 can again be energized is sufiicient to permit lamps9 in the lighting circuit to cool down so that they may be restarted attheir cold starting voltages. If, however, upon re-energization oflighting circuit 1 no current flows therein, then protective timer 20-21will operate to disconnect the lighting circuit from its source ofsupply and require resetting before the lighting circuit can beenergized again.

Thus, recycling of the circuit provides for re-ignition of the directseries connected lights when their extinguishrnent resulted from a dipin line voltage or a similar line disturbance, the circuit beingautomatically re-energized after a sufiicient time delay to preventpremature cutout failures occurring across lamps having a high startingvoltage as a result of their heated condition resulting from previousoperation. On the other hand, any fault causing an open circuit whichproduces clangerously high open circuit voltages, causes the lightingcircuit to be de-energized after a short time delay in response to theoperation of protective timer 20-21. One advantage of this circuit isthat the time delay reclosing relay 22 is not inserted into the circuituntil the lamps have started. Therefore, any fluttering of contacts inthe circuit or any other primary circuit disturbances will not causemisoperation of the circuit. Furthermore, once the lamps have started,any primary circuit disturbances which will not put the lamps out willnot cause recycling and consequently recycling of the system is limitedto only the necessary number of operations and is strictly dependent onthe stability of the lamps under the conditions of the circuit. Afurther advantage of this circuit is that the protective timer 2G-21will operate to prevent excessive voltages in the lighting circuit inthe event that a failure of current to flow therein is due to a faultthat requires correction before re-energizing the lighting circuit.

From the operations above described, it will also be apparent that afailure of the power supply will impose the necessary time delay beforean attempt is made to restart the lamps, since such restarting operationcannot occur until contacts 33 of the time delay reclosing relay 22 hascompleted the control circuit for the operating winding 3 of thecontactor 7.

The control system shown in Fig. 2 is substantially the same as thatshown in Fig. 1 with the exception that a timer 44 requiring manualresetting has been substituted for the electrical reset timer 20-21 ofFig. 1. Consequently, in Fig. 2 like reference numbers have beenemployed to identify parts therein corresponding with parts previouslydescribed in connection with Fig. 1.

Thermal switch 44 is a toggle switch having an operating lever 45provided with a handle and pivoted upon a pin 46, a trip member 47pivoted upon this pin and a contact operating arm 48 also pivoted onthis pin. A toggle spring 49 connected between operating lever 45 andcontact arm 48 moves this contact arm into an upward position so that acontact 50 mounted on this arm engages a contact 51 within a shield 52when the operating lever and its handle are moved to an upper position.Trip member 47 is held in position by a thermostatic element 53, thefree end of which engages a trigger 54 on trip member 47. At normaltemperatures the thermostatic element catches trigger 54 and holds tripmember 47 stationary against the pressure of rod 55 which is urgeddownwardly by a spring 56'. When the thermostatic element is heated bycurrent flowing through trip member 47 about pin 46 in a ciockwisedirection.

The trip member in turn engages a tripping lug 57 on arm 48 and carriesthis arm in a clockwise direction against the pull of spring 49 to opencontacts 50, 51. Switch 44 is reset by first moving lever 45counterclockwise, the lever being provided with a projection 58 whichengages and carries trip member 46 along with it. The trip member is somoved until trigger 54 is engaged by thermostatic element 53. Tripmember 47 is then held in its normal position by the thermostat. Lever49 is thereafter moved clockwise to its uppermost position, theover-center spring 49 being moved past pivot 46 and arm 49 being raisedto close the circuit of contacts 50, 51.

Thermostatic element 53 is heated by current supplied by a secondarywinding 59 of a transformer 69. The circuit may be traced from oneterminal of winding 59 through the thermostatic element 53 and contacts50, 51 to the other terminal of this winding. The primary winding 61 oftransformer 60 is connected across energizing conductors 39 throughswitch 38, contacts 33 of time delay reclosing relay 22, an adjustableresistor 62 and contacts 14 of series relay l1. Resistor 62 provides atiming adjustment for thermal switch 44. When switch 44 is tripped bythermostatic element 53, contacts 50, 51 open the circuit of thethermostat and the handle of lever 45 of switch 44 releases contacts 63to open the circuit of the operating winding 8 of contactor 7 in thesame manner as control contacts 29 of lock-in relay 21 of Fig. l. Thethermalswitch 44 and its operating circuits are the same as those shownin the above-referred to United States Letters Patent 2,324,875 whichmay be considered for further detailed information relative thereto.

In view of the several operations described above in connection withFig. 1, it is believed to be quite obvious that the same operations willoccur when using the circuit of Fig. 2 with the exception, of course,that thermal switch 44 must be reset by adjusting its linkage at thelocation of this switch whereas the corresponding timing mechanism 26-21of Fig. 1 can be reset electrically at a remote location by opening andagain closing control switch 38.

Systems embodying our invention provide the overvoltage protectionrequired in series lighting circuits and at the same time also preventpremature cutout failures occurring across lamps having a highrestarting voltage while still hot from a previous operation which wasinterrupted due to circuit disturbances resulting in an extinguishmentof one or more lamps in the lighting circuit. In other words our systemprevents a protective de-energization of a series lighting circuitimmediately following an interruption in the current ilow therein andprovides for such protective de-energization if energization or reenergization of the circuit produces no current flow there- While wehave described above only two preferred em bodiments of our invention byway of illustrating the same, many modifications will occur to thoseskilled in the art, and we, therefore, wish to have it understood thatwe intend in the appended claims to cover all such modifications as fallwithin the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A control system comprising: supply conductors; load conductors;switching means for controlling the connection of said supply conductorswith said load conductors; a control circuit, the closing and opening ofwhich respectively operates said switching means to connect anddisconnect said load conductors with said supply conductors; firsttiming means for opening said control circuit a predetermined timeinterval after its energization when no current exists in said loadconductors; second timing means responsive to an interruption in currentflow in said load conductors for opening said control circuit 8 andagain closing it after a predetermined time; and means for opening andclosing said control circuit independently of but subject to the controlof each of said timing means.

2. A control system including load conductors; supply conductors; acontactor having normally open contacts and'means including a windingfor operating said contacts; means including said normally open contactsof said contactor for connecting said lead conductors with said supplyconductors; first timing means for energizing said winding of saidcontactor and for in. rrupting the energization of said winding of saidcontactor a predetermined time interval after its energizatiou when nocurrent exists in said load conductors; and second timing means forcompleting the energizing circuit for said winding of said contactorwhile current flows in said load conductors, for interrupting saidenergizing circuit upon interruption of current flow in said loadconductors, and for again completing said energizing circuit apredetermined time period thereafter.

3. A control system including load conductors; supply conductors; acontactor having normally open contacts and means including a Windingfor operating said contacts; means including said normally open contactsof said contactor for connecting said load conductors with said supplyconductors; first timing means energized concurrently with theenergization of said winding of said contactor and responsive to acondition of no current flow in said load conductors for interruptingand maintaining interrupted the energization of said winding of saidcontactor after a predetermined time interval; and a second timing meansfor completing the energizing circuit for said windnig of said contactorwhile current flows in said load conductors, for interrupting saidenergizing circuit upon interruption of current flow in said loadconductors, and for again completing said energizing circuit apredetermined time period thereafter.

4. A control system comprising supply conductors; load conductors; acontactor having normally open contacts and means including a windingthe energization of which closes said contacts; means including saidcontacts of said contactor for connecting said load conductors to saidsupply conductors; a series relay having normally closed contacts,normally open contacts, and means including an operating winding foractuating said contacts; means for connecting the operating winding ofsaid series relay to be responsive to current flow in said loadconductors; first timing means including the normally closed contacts ofsaid series relay in their closed position for de-energizing andmaintaining de-energized said operating winding of said contactor inresponse to no current flow in said load conductors a predetermined timeinterval after said operating winding of said contactor has beenenergized; and second timing means including the normally open contactsof said series relay for maintaining energization of said winding ofsaid contactor upon closure of said last mentioned contacts and forde-energizing said winding of said contactor for a predetermined timeinterval upon opening of said last mentioned contacts.

5. A control system comprising supply conductors; load conductors; acontactor having normally open contacts and means including a winding.the energization of which closes said contacts; means including saidcontacts of said contactor for connecting said load conductor to saidsupply conductors; a series relay having normally closed contacts,normally open contacts, and means including an operating winding foractuating said series relay contacts; means for connecting the operatingwinding of said series relay to be responsive to current flow in saidconductors; first timing means including the normally closed contacts ofsaid series relay in their closed position for de-energiz ing saidoperating winding of said contactor in response to no current flow insaid load conducotrs a predetermined time interval after said operatingwinding of said contactor has beenenergized; and second timing meansincluding the normally open contacts of said series relay 9 formaintaining the energization of said winding of said contactor uponclosure of said last mentioned contacts and for de-energizing saidwinding of said contactor for a predetermined time interval upon openingof said last mentioned contacts.

6. A control system comprising a constant current translating devicehaving input and output terminals; load conductors connected to theoutput terminals of said device; a contactor having normally opencontacts and means including a winding for operating said contacts;supply conductors connected to the input terminals of said devicethrough said contacts of said contactor; a control circuit in serieswith said winding of said contactor; means including a switch in saidcontrol circuit for connecting said control circuit to said supplyconductors and for controlling the energization of said winding of saidcontactor through said control circuit; firsttiming means for energizingsaid winding of said contactor and responsive to a condition of nocurrent flow in said load conductors for interrupting said controlcircuit independently of said switch a predetermined time interval afterenergization of said contactor winding; and second timing means forcompleting said control circuit while current flows in said loadcircuit, for interrupting said control circuit independently of saidswitch upon an interruption of current flow in said load conductors, andfor again completing said control circuit after a predetermined timeinterval.

7. A control system comprising a constant current translating devicehaving input and output terminals; load conductors connected to theoutput terminals of said device; a contactor having normally opencontacts and means including a winding for operating said contacts;supply conductors connected to said input terminals of said devicethrough said contacts of said contactor; a control circuit in serieswith said winding of said contactor; means including a switch in saidcontrol circuit for connecting said control circuit to said supplyconductors and for controlling the energization of said winding of saidcontactor through said control circuit; first timing means energizedconcurrently with the energization of said winding of said contactor andresponsive to a condition of no current flow in said load conductors forinterrupting said control circuit independently of said switch after apredetermined time interval; and second timing means for completing saidcontrol circuit while current flows in said load circuit, forinterrupting said control circuit independently of said switch upon aninterruption of current flow in said load conductors, and for againcompleting said control circuit after a predetermined time interval.

8. A control system comprising a constant current translating devicehaving input terminals and output terminals; load conductors connectedto said output terminals of said device; supply conductors; a contactorhaving normally opened contacts connected between said supply conductorsand said input terminals of said translating device and means includinga winding for actuating said contacts; a timing relay having normallyclosed contacts and means including an operating winding and a delaymechanism for immediately opening said contacts upon energization ofsaid winding and thereafter upon de-energization of said winding closingsaid contacts after the lapse of a predetermined time intervaldetermined by said delay mechanism; a holding relay having meansincluding an opertaing winding, normally open contacts connected inshunt to said normally closed contacts of said timing relay, andnormally open contacts connected in circuit with said operating windingof said timing relay in shunt to the operating winding of said holdingrelay; means including a second timing relay having normally closedcontrol contacts, normally closed reset contacts, and an operatingcircuit for opening both of said control and reset contacts after apredetermined time interval following energization thereof; a seriesrelay having normally closed contacts controlling the energization ofsaid operating circuit of said second timing relay, normally opencontacts controlling the energization of said operating windings of saidfirst timing relay and of said holding relay, and means including anoperating winding connected to be responsive to current flow in saidload conductors for actuating said series relay contacts; a controlcircuit including the normally closed control contacts of said firsttiming relay, the operating winding of said contactor and the normallyclosed control contacts of said second timing relay; and means forcontrolling the energization of said control circuit to control theenergization of said operating winding of said contactor.

9. A control system comprising a constant current translating devicehaving input and output conductors; supply conductors; load conductorsconnected to said output conductors of said translating device; acontactor having normally open contacts and means including a windingfor operating said contacts; means including said contacts of saidcontactor for controlling the connection of said input conductors ofsaid translating device with said supply conductors; a series relayhaving normally open contacts, normally closed contacts and means including a winding for operating said series relay contacts; means forconnecting said winding of said relay in series circuit relation withsaid load conductors; a timing relay having normally closed contacts andmeans including an operating winding and a time delay mechanism forinstantaneously opening the contacts of said timing relay when its saidoperating winding is energized and for delaying the closure of saidcontacts for a predetermined interval determined by its said time delaymechanism upon de-energization of its said operating winding; a holdingrelay having means including an operating winding, normally opencontacts connected in shunt with said normally closed contacts of saidtiming relay, normally open contacts which connect the winding of saidtiming relay in shunt to said holding relay winding; control conductors,means including a switch for connecting said control conductors to saidsupply conductors; a thermal switch having normally closed contacts incircuit with a thermal element and normally open contacts which areclosed by a predetermined heating of said thermal element which alsoopens its normally closed contacts; and a lock-in relay having: normallyclosed control contacts connecting said winding of said contactor incircuit with said normally closed contacts of said timing relay acrosssaid control conductors and connecting said winding of said holdingrelay across said control conductors in circuit with said normallyclosed contacts of said timing relay and said normally open contacts ofsaid series relay; normally closed reset contacts connected in circuitwith said normally closed contacts of said series relay, said thermalelement, said normally closed contacts of said thermal switch and saidnormally closed contacts of said timing relay across said controlconductors; and normally open lock-in contacts connected in shunt acrosssaid normally open contacts of said thermal switch, said lock-in relayhaving means including a winding for operating its said contacts, andsaid lock-in relay winding being con nected across said controlconductors through said normally opened contacts of said thermal switchand said normally closed contacts of said timing relay.

10. A control system for operating switching means for controlling theconnection of supply conductors with load conductors comprising: acontrol circuit, the closing and opening of which respectively operatessaid switching means to connect and disconnect said load conductors withsaid supply conductors; first timing means effective after apredetermined time interval for opening and holding open said controlcircuit when no current exists in said load conductors; second timingmeans effective immediately after an established current in said loadconductors ceases to exist for opening said control circuit andpreventing operation of said first timing means 1 l and effective apredetermined time interval thereafter for reclosing said controlcircuit and permitting-operation of said first timing means. V a 1 V 11.A control system for operating switching means for controlling theconnection of supply conductors with load conductors comprising: acontrol circuit, the closing and opening of which respectively operatessaid switching means to connect and disconnect said load conductors withsaid supply conductors; first timing means effective a predeterminedtime interval after said control circuit is energized for opening andholding open said control circuit when no current exists in said-loadconductors; second timing means effective when current ceases to existin said load conductors for opening said control circuit and preventingoperation of said first timing means fora predetermined time intervalthereafter.

12. A control system for operating switching means for controlling theconnection of supply conductors with load conductors comprising: acontrol circuit, the closing and Opening of which respectively operatessaid switch ing means to connect and disconnect said load conductorswith said supply conductors; first timing means effective apredetermined time interval after being energized for opening andholding open said control circuit; sec ond timing means for opening saidcontrol circuit and de-energizing said first timing means immediatelyupon de-energization of said second timing means and for retiming meansa predetermined time interval thereafter; means for supplyingenergization to said control circuit and to each of said timing means;and means for interrupting said energization to said first timing meansonly when current exists in said load conductors and for interruptingsaid energization to said second timing means only when no currentexists in said load conductors.

13. A control system for operating switching means for controlling theconnection of supply conductors with load conductors comprising: acontrol circuit, the closing and opening of which respectively operatessaid switching means to connect and disconnect said load conductors withsaid supply conductors; first timing means including a delay circuitefieetive a predetermined time interval after being closed to cause saidfirst timing means to open and hold open said control circuit; secondtiming means for opening said control circuitand said delay circuitimmediately upon de-energization of said second timing means and forreclosing said control circuit and said delay circuit a predeterminedtime interval thereafter;

means effective only during a condition of no current existing in saidload conductors for holding open said delay circuit to prevent theoperation of said first timing means and for maintaining said secondtiming means deenergized.

No references cited.

